Tumble drying processes are a mainstay of both domestic and industrial textile fabric cleaning procedures and typically involve placing the textiles in a container such as a perforated cylindrical drum which is rotated in alternating clockwise and anti-clockwise cycles whilst hot air is introduced into the drum through the perforations. A combination of the hot air treatment and the mechanical action of the tumbling process causes water to be expelled from the textile materials in order that drying is achieved.
However, such processes, though generally very effective, are usually characterised by high levels of energy consumption, both in terms of effecting rotation of the container and, most particularly, in generating heated air. Typically, prior art processes may involve prolonged treatments at high temperatures in order to effect the required degree of drying. Clearly, however, the lower are the energy requirements of a system, the more efficient is the system and its associated drying process. Consequently, there is a desire to reduce both the time of such drying treatments and the temperature at which they are carried out in order to provide more efficient processes, whilst maintaining equivalent drying performance.
Current efficient domestic tumble dryers are graded in terms of energy consumption according to EU Directive 92/75/EEC and, more specifically, Directive 95/13/EEC, with category ‘A’ dryers being the most efficient, and category ‘G’ the least efficient. Hereinafter, energy consumptions are quoted for the cotton drying cycle for each machine type, in kWh/kg of drying load. Thus, for vented tumble dryers, ‘A’ class consumption is <0.51 kWh/kg, ‘C’ class (most common) is between 0.59 and 0.67 kWh/kg, whilst ‘G’ class is >0.91 kWh/kg. These values differ slightly for condenser tumble dryers, with ‘A’ class at <0.55 kWh/kg, ‘C’ class (most common) at between 0.64 and 0.73 kWh/kg, and ‘G’ class at >1.00 kWh/kg. With average domestic dryer capacities now at around 8.0 kg, this equates to a typical consumption for a ‘C’ class vented tumble dryer of 4.7-5.4 kWh/cycle; an ‘A’ class equivalent machine would run at <4.1 kWh/cycle. Some vented domestic dryers are now capable of performing beyond this lower limit and, at the time of writing, the energy labelling system in the European Union is being adjusted in line with this, such that tumble dryers will soon move to A+ and A++ labels. Performance levels in the domestic sector generally set the highest standard for an efficient fabric drying process. Energy consumption in industrial tumble drying is usually higher, due to the need for faster cycle times. It is also noteworthy that, overall, tumble drying is significantly less efficient than washing as a component part of the laundry process in either sector.
Heating of the circulating air is the principal use of energy in such tumble dryers and the present inventors have therefore sought to effect improvements in the prior art processes by reducing the temperature levels required in such processes. This has been possible by means of changes made to the mechanical action of the process on the fabric in the drying load. Mechanical action in a conventional, horizontal axis tumble dryer is generated by the forces acting on the fabric through falling and hitting either other fabric or the dryer inner drum surface, whilst the fabric is interacting with the forced hot air flow. This results in release and evaporation of water from within the fabric, and hence drying. In the method herein provided, alteration of the mechanical action of the process in order to promote more localised release and evaporation of water at the fabric surface has resulted in lower drying temperatures. As a further potential benefit, it has been found that the changes made can also reduce the degree of fabric folding, and hence the level of creasing associated with tumble drying. Creasing, which concentrates stresses during this drying process, is a major source of localised fabric damage. Ironing at high temperatures is then the conventional means used to remove such creasing and this, too, brings a fabric damage penalty. Prevention of fabric damage (i.e. fabric care) is of primary concern to the domestic consumer and the industrial user. Furthermore, if creasing is reduced, there is also the secondary benefit to the user of convenience resulting from less ironing.
Hence, the present inventors have sought to devise a new approach to the drying problem, which allows the above deficiencies associated with the methods of the prior art to be overcome. The method which is provided eliminates the requirement for the use of high drying temperatures for extended periods of time, but is still capable of providing an efficient means of water removal, so yielding economic and environmental benefits. The method which is provided also promotes fabric care through reduced creasing and fewer requirements for subsequent ironing.
In WO-A-2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. In preferred embodiments, the substrate comprises a textile fibre and the polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, but are most preferably in the form of nylon particles.
The method disclosed in this prior art document has been highly successful in providing an efficient means of cleaning and stain removal which also yields significant economic and environmental benefits due to its use of a cleaning formulation which requires the use of only limited amounts of water. The present inventors have now sought to provide a drying process which adopts a similar approach to that disclosed in WO-A-2007/128962, and which offers benefits in terms of reduced energy requirements, whilst still providing an acceptable level of performance, and have succeeded in achieving at least equivalent drying performance whilst employing significantly reduced process temperatures. Thus, a process is provided wherein the drying effect achieved as a consequence of mechanical interaction of a wet substrate with physical media is optimised, such that excellent drying performance may be achieved at much lower temperatures (i.e. low energy) without extending drying times. Additional benefits have also been observed in terms of the reduction of fabric creasing and associated fabric damage.